The Intracellular Concentration of Bound and Unbound Magnesium Ions in Escherichia coli

The concentration of magnesium ions in solution within Escherichia coli ML 35 was found to be the same as the extracellular concentration over a range of 10-6 m to 10-2 m. Since growth rate was unaffected at 4 x 10-5 m, it was concluded that protein synthesis in vivo is accomplished at much lower concentrations of magnesium than is required for protein synthesis in vitro. Ribosome-bound spermidine, but not putrescine, was found to vary inversely with ribosome-bound magnesium. It is proposed that polyamines, especially spermidine, may be more important for protein synthesis in vivo than is magnesium.